Ecosystems and habitats

The Australian continent supports a vast array of ecosystem types. Australia’s bioregion framework recognises 89 regions and 419 subregions based on common climate, geology, landform, native vegetation and species information, all of which are described in the Interim Biogeographic Regionalisation for Australia (see the Native vegetation section in the Land chapter). The bioregions and subregions are the reporting units for assessing the status of native ecosystems and their levels of protection in the National Reserve System (see Protected areas).

Globally, land-use change has had the largest impact on ecosystems: 75% of Earth’s land surface has been significantly altered by human pressures (IPBES 2019). Climate change is exacerbating the impact of land-use change and other pressures on ecosystems (IPBES 2019).

The endpoint of disruption and degradation of ecosystems is irreversible collapse – when key defining features and functions of the ecosystem are lost. At least 19 Australian ecosystems have been reported to show signs of collapse or near-collapse, although none has yet collapsed across its entire distribution (Bergstrom et al. 2021). Ecosystems experiencing collapse span the Australian continent and include Antarctic and subantarctic ecosystems (Figure 21).

All 19 Australian ecosystems reported to be showing signs of collapse experience multiple pressures, including 12 that experience more than 10 pressures. In recent years, pressures have become more severe, widespread and more frequent. Nine ecosystems have recently experienced pressures unprecedented either in severity or spatial scale, relative to historical records (Bergstrom et al. 2021).

Habitat modification or destruction has occurred in 18 ecosystems, often at substantial levels. Climate change, primarily change in temperature, is a key pressure for 18 ecosystems, while invasive species affect 12 ecosystems, storms affect 13 ecosystems and fires affect 12 ecosystems. Assessing the risk of collapse of ecosystems provides vital understanding about the root causes of decline and potential methods for recovery.

The Land chapter provides a detailed assessment of terrestrial ecosystem extent and condition (see the Land chapter). The state of native vegetation is described as mostly poor and deteriorating, with many native ecosystems having been extensively cleared and a large proportion of habitats degraded.

Figure 21 Locations of ecosystems experiencing collapse

Threatened ecological communities

Threatened ecological communities are ecosystems in danger of being lost due to some threatening process, and that have been identified and listed under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) or state legislation. Under the EPBC Act, threatened ecological communities can be listed as Vulnerable, Endangered or Critically Endangered. However, only threatened ecological communities that are Endangered or Critically Endangered are considered to be ‘matters of national environmental significance’ under part 3 of the EPBC Act. As a result, impacts from new development to vulnerable threatened ecological communities need not be referred to the Australian Government for assessment (Simmonds et al. 2020).

As of June 2021, 87 threatened ecological communities were listed under the EPBC Act: 41 are Critically Endangered, 44 are Endangered and 2 are Vulnerable. Since January 2016, there have been 14 new listings, including 9 in the Critically Endangered category (Figure 22).

Most listed threatened ecological communities occur in areas that have been heavily modified for agriculture or urban development. Ten of the new listings since 2016 occur in New South Wales, south-east Queensland and Victoria, 2 occur on the Swan Coastal Plain of Western Australia, and 1 each occur in South Australia and Tasmania.

Figure 22 Cumulative number of threatened ecological communities listed under the EPBC Act

The approach for listing on the International Union for Conservation of Nature (IUCN) Red List of Ecosystems is similar to the assessment process for ecosystems under the EPBC Act and consistent with assessments made according to the IUCN Red List of Species. The IUCN criteria have been used to assess 18 Australian ecosystems; 3 assessments were undertaken or led by the IUCN, and a further 15 were undertaken regionally in Australia. Since 2016, 1 ecosystem has been added to the IUCN Red List: the Oyster Reef Ecosystem of Southern and Eastern Australia. The overall assessment for that ecosystem ranks the risk of collapse as Critically Endangered, with a high degree of confidence (Gillies et al. 2020) (see the Marine chapter).

Soil ecosystems and biodiversity

Soils are fundamental to primary production, decomposition, and nutrient, carbon and water cycles. Below-ground organisms comprise a large fraction of global terrestrial diversity and are responsible for essential ecosystem functions and services, such as plant productivity, nutrient cycling, organic matter decomposition, pollutant degradation and pathogen control (Delgado-Baquerizo et al. 2020).

Soil microbes are vital for ecosystem health, supporting soil fertility, species diversity and resilience in natural ecosystems. Soil microbial communities and overlying vegetation are closely linked (Hamonts et al. 2017) (see case study: Vegetation cover as a national indicator of soil condition and erosion risk, in the Soil health section in the Land chapter). Soil biodiversity is also increasingly recognised as being linked to human health and wellbeing because it can suppress disease-causing soil organisms and influences the quality of food, air and water (Wall et al. 2015). Land degradation causes a decline in soil microbial activity, and agricultural practices have strong impacts on microbial community composition (Gellie et al. 2017).

Pressures on soil ecosystems are immense. Some 45% of the nation’s soil is used for agricultural production, with 84% of this used for grazing, 8% for cropping, and the remainder for forestry and other practices. Demands on soil resource are increasing, such as needing to produce more food and at the same time sequester carbon to mitigate climate change (Bennett et al. 2019). The Land chapter describes the condition of soil in Australia as ‘poor’ and ‘deteriorating’, based on reductions in below-ground carbon, continued erosion and reduced groundcover (see the Land chapter).

The soil microbiome is one of the most genetically and ecologically diverse communities on Earth, but is poorly understood. However, metabarcoding of environmental DNA (eDNA) (see case study: Genetic approaches to information gathering) is increasingly proving to be an effective and efficient method to survey important groups such as soil bacteria and fungi where morphological identification is notoriously problematic. For example, scientists have recently used eDNA techniques to demonstrate the return of the native soil bacterial community in revegetated areas (Gellie et al. 2017, Yan et al. 2020).

The Australian Microbiome Initiative is a continental-scale, collaborative project aspiring to characterise the diversity and ecosystem service provision of the microorganisms inhabiting natural Australian ecosystems. It is collecting DNA sequence information about microbial community composition across a range of different sites to create a reference map of Australia’s soil (see the Soil section in the Land chapter).

Aquatic ecosystems and habitats

The widespread rainfall deficiencies across Australia from 2017 to 2019, accompanied by high maximum and minimum temperatures, saw a return to drought conditions over much of Australia (see the Climate chapter). These conditions had a significant impact on the quantity and quality of surface water, recharge of groundwater resources, terrestrial aquatic environments, and Indigenous water values and cultural flows. Streamflows in most rivers across south-eastern Australia were lower than average, with many rivers recording their lowest flows on record. However, heavy rainfall across the Upper Diamantina and Georgina River catchments in early 2019 generated run-off into Kati Thandi / Lake Eyre Basin. Although 2020 saw many coastal areas around Australia recovering from the drought conditions of the previous years, the Murray–Darling Basin continued to experience drought.

The Inland water chapter describes changes in water flows in Australian catchments since 2016 (see the Inland water chapter).

Australia’s freshwater ecosystems and biodiversity face many pressures from humans. In much of Australia, especially the south-east, the greatest threat is the modification of water processes that has resulted from river regulation, surface water and groundwater extraction, and other water resource developments. Altered water flows, of both surface waters and groundwaters, has resulted in further changes to water and soil quality, including salination and acidification from the exposure of sulfidic sediments (Capon et al. 2017). Other pressures include barriers to fish movement, invasive species, habitat loss and alteration, and commercial and recreational fishing (Koehn et al. 2020b).

The Murray–Darling Basin spans a large area of south-eastern Australia, and is of significant environmental, cultural and economic value to Australia. It is home to 16 internationally significant wetlands, 35 endangered species and 98 different species of waterbirds. More than 2.2 million people live in the Basin, including people from 40 First Nations, and more than 4 million people depend on the Basin for everyday water needs. Basin rivers and catchments are mostly in poor and very poor condition (see the Inland water chapter), and native fish populations have declined by more than 90% in the past 150 years – a trend that appears to be continuing today (Koehn et al. 2020a).

Surface water diversions and extensive river regulation, combined with climate change, have resulted in major changes to flow and flood regimes for rivers and wetlands in the Basin. The Commonwealth Water Act 2007 legislates for conservation of the Basin Ramsar wetlands and enacts this through the Murray–Darling Basin Plan, a statutory instrument under the Water Act for returning water to the environment by reducing the amount taken for irrigation and other consumptive uses. The environmental objectives of the Basin Plan are to protect and restore flow-, flood- and groundwater-dependent ecosystems (or ‘water-dependent ecosystems’ including rivers, lakes, flood plains and other wetlands) and their ecosystem functions, and ensure that they are resilient to climate change and other threats. The Basin-wide Environmental Watering Strategy (MDBA 2019) provides details of how the environmental objectives of the Basin Plan are to be implemented, including expected outcomes for river flows and connectivity, native vegetation, waterbirds, and fishes.

The 2020 Basin Plan evaluation found that its implementation over the previous 7 years was ‘having a significant and positive impact on the Basin environment’ (MDBA 2020). Environmental water has supported periods of re-connection of isolated reaches along river channels, and freshwater ecosystems receiving environmental water benefited from flows, with measurable improvements for flow-dependant ecosystems and species following individual watering events (Cosier et al. 2017). However, other reports have highlighted a major shortfall in restoring river flows to wetlands (Colloff et al. 2020), and the very limited monitoring of aquatic ecosystems has mostly highlighted temporary localised positive responses (Chen et al. 2020). For example, the extent, magnitude and duration of flooding of wetland woody vegetation communities is considered to be inadequate, in most cases, to meet the ecological requirements needed to maintain their extent and condition (Chen et al. 2020).

Assessments of the state and trend of threatened species in the Basin is limited to flow-dependent fish and waterbirds, and these assessments tend to be species-specific, with a focus on particular regions. Recent assessments have shown positive outcomes for some threatened species in some locations at some points in time, but monitoring and reporting on the state and trend of threatened species in the Basin is largely inadequate for assessing whether the Basin Plan is achieving its environmental objectives (Ryan et al. 2021).

Case Study Remediating erosion after bushfires

The NSW South Coast was hit hard by the January 2020 bushfires. Heavy rains immediately after the fires resulted in ashy sediment flowing rapidly into the estuaries.

With a bushfire recovery grant, Local Land Services and the Mogo and Batemans Bay Local Aboriginal Land Councils joined forces to fortify areas of high run-off in the catchments of the Clyde and Deua rivers. The team installed 300 ecologs made from 100% coconut fibre compacted into an outer mesh of bristle coir twine and jute mesh (Figure 23).

This successful project has helped alleviate damage to aquatic ecosystems, including valuable areas such as saltmarsh, mangroves and seagrass beds that provide fish habitat and are a food source.

Figure 23 Batemans Bay Local Aboriginal Land Council Ranger Group working in the Clyde Catchment to reduce effects of sedimentation on waterways

Photo: James Cornwell, Local Land Services, New South Wales

Wetlands and billabongs

There are nearly 34 million hectares of wetlands in Australia (see the Inland water chapter), covering 4.4% of the continent (Bino et al. 2016), about half of which is floodplains and swamps. Wetlands support relatively high numbers of species found nowhere else, which are at risk of extinction (Silcock & Fensham 2018).

The Convention on Wetlands of International Importance (the Ramsar Convention) is a global environmental treaty that aims to provide a framework for promoting the conservation and wise use of wetlands and their resources. Australia has 65 Ramsar sites, covering more than 8.3 million hectares (Bino et al. 2016). Wetlands often are disproportionately affected by changes in agricultural and urban landscapes (Bino et al. 2016). They have been extensively cleared, sown to pasture species, had their flows altered, and been subject to concentrated grazing pressure and weed invasion. They are also vulnerable to further hydrological changes and drying under future climate change scenarios (Finlayson et al. 2017). The return to drought conditions since 2016, in conjunction with increased consumptive water use, has resulted in decreased flows into wetlands and reduced inundation (see case study: Filling of Narran Lakes/Dharriwaa, in the Wetlands section in the Inland water chapter).

Wetland ecosystems hold significant ecological, recreational, spiritual, cultural and economic significance for Indigenous Australians. In some areas of central and northern Australia, wetlands and billabongs are particularly threatened by invasive feral ungulates, including water buffalo, pigs and cattle. Researchers have been working with the Ngukurr Yangbala Indigenous rangers in the South East Arnhem Land Indigenous Protected Area to describe changes in billabong condition related to feral ungulate disturbance and the cultural impacts on local Indigenous people (Russell et al. 2021). Indigenous knowledge holders revealed that, historically, yarlbun (water lily) grew in billabongs year-round and was a staple part of people’s diets. However, since the introduction of hard-hooved ungulates and their subsequent proliferation and invasion, Indigenous people report substantial declines in the yarlbun cover of billabongs in the late dry season, when water resources become scarce and animals concentrate around the persisting billabongs. Indigenous ecological knowledge suggests that some billabongs have passed an ecocultural threshold indicated by a shift from a yarlbun-dominated system to a turbid, sediment-dominated system driven by feral ungulates (Ens et al. 2016, Russell et al. 2021).

Assessment Aquatic ecosystem condition
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.
Adequate confidence

Aquatic ecosystem condition depends on the location of the ecosystem, with ecosystems in more populated regions experiencing higher pressures than those in less populated regions. Related to United Nations Sustainable Development Goal targets 6.6, 15.1, 15.5

Assessment Aquatic ecosystem condition – northern and central Australia
2021 Assessment graphic showing the environment is in good condition, resulting in stable environmental values, and the situation is stable.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing the environment was in good condition, resulting in stable environmental values, and the situation was stable.

Pressures on aquatic ecosystems in northern and central Australia are largely associated with feral animals and invasive weeds. Some localised areas experience significant very high impacts; however, in most places, impacts tend not to persist because of the episodic nature of rainfall and flow events. Aquatic ecosystems in these areas generally maintain minimum expected function, although there is reduced function, or even persistent transformation, in some localised areas.

Assessment Aquatic ecosystem condition – southern, eastern and south-western Australia
2021 Assessment graphic showing the environment is in very poor condition, resulting in heavily degraded environmental values, and the situation is deteriorating.
Adequate confidence
Assessment graphic from 2011 or 2016 showing the environment was in poor condition, resulting in diminished environmental values, and the situation was deteriorating.

Pressures on aquatic ecosystems in southern, eastern and south-western Australia are persistent and extensive, resulting in very poor condition and reduced ecological function. Drought and fires over the past 5 years have compounded pressures from invasive species and human activities. River regulation and water abstraction place significant pressure on aquatic ecosystems in this area of Australia.